Using a mandolin, carefully slice ginger (paper thin) and then radishes; place radish slices in jars and set aside. Place sliced ginger in a pot of boiling water and process for 7 to 8 minutes. Drain well before sprinkling with salt; let it sit for 30 minutes. Dry the slices with paper towels before transferring them to the jars with radishes.
In a small pot over medium heat, combine rice vinegar with granulated sugar; stir until sugar dissolved. Increase the heat to medium-high and bring vinegar mixture to a boil. Pour immediately over the ginger slices in the prepared jars.
Let the jars cool, stirring occasionally without disturbing the radishes at the bottom. Close the lid and transfer to the fridge. About 8 to 12 hours later, remove the discolored radish slices from the jars and discard them. Place jars back in the refrigerator until ready to serve. It keeps for 2 months. Makes 2 -250 ml jars.